The present invention relates to a controller for a vehicle air conditioner, and more particularly to such a controller that adjusts the evaporator temperature setting depending on operating conditions.
A vehicle air conditioner generally has an engine-driven compressor for compressing a coolant, a condenser, and an evaporator. Such an air conditioner is controlled by its on/off operation of the compressor. The on/off operation of the compressor is determined by both an evaporator blowoff temperature set value, which is responsive to the evaporator inlet temperature, etc., and the actual evaporator blowoff temperature. Thus, the compressor on/off operation is controlled independently of the engine operating status, except for certain conditions such as during quick acceleration, i.e., large throttle openings.
One example of a controller for a vehicle air conditioner is disclosed in Japanese Unexamined Patent Application Publication No. 8-295131. The air-conditioner, which is driven by an internal combustion engine, includes a compressor and an electromagnetic clutch. An electronic control unit (ECU) engages and disengages the electromagnetic clutch depending on the engine operating status, thereby controlling the operation of the air conditioner. The ECU also controls each fuel injector to cutoff fuel during engine deceleration. When executing fuel cutoff during engine deceleration, the ECU also disengages the electromagnetic clutch to disconnect the compressor from the engine, whereby the air conditioner is stopped and air conditioning operation is cut off. After the fuel cutoff operation, the ECU prevents the cutoff of the air conditioning operation for a predetermined period, i.e., air conditioning operation is enabled. As a result, satisfactory air conditioning is maintained without deteriorating fuel consumption during either deceleration of the internal combustion engine or a quick increase of load.
In the conventional air-conditioner, when the compressor is turned on in the coasting mode, deceleration increases and drivability worsens due to the draw of the compressor, particularly when a transmission device, such as an engine brake, is engaged.
Another disadvantage is that increased deceleration lowers vehicle speed more quickly and the driver must re-accelerate (via the accelerator pedal) more often, deteriorating, i.e., increasing, fuel consumption.
On the other hand, during braking when the transmission device and the compressor are engaged, the compressor is driven by and uses the kinetic energy of the vehicle, thereby assisting in braking. If the compressor is not engaged during braking, this kinetic energy would not be utilized but instead would be emitted as heat from the braking device. Thus, fuel consumed driving the compressor on subsequent acceleration would be greater than if the compressor had been engaged during braking, and overall fuel consumption is worsened.
The present invention provides a controller for a vehicle air conditioner. The air conditioner comprises an engine-driven compressor, a condenser, and an evaporator. The controller comprises a control unit adapted to control blowoff temperature according to an evaporator temperature setting calculated from an evaporator inlet temperature, a fuel cutoff control unit, an engine rpm detecting unit, and a brake signal detecting unit. The control unit is also adapted to decrease the evaporator temperature setting during fuel cutoff operation by the fuel cutoff control unit when a change of the engine rpm within a certain time period is less than a predetermined value, and when a brake signal is detected by the brake signal detecting unit and this signal is continued for a predetermined time.
By raising the evaporator temperature setting under these conditions, the time period for which the compressor is disengaged (stopped) increases. This reduces engine load and moderates vehicle deceleration. This also increases the duration of fuel cutoff and, thus, reduces fuel consumption.
The control unit may also lower the evaporator temperature setting during fuel cutoff operation under these same conditions which would allow the compressor to operate for a longer time and would increase engine braking during braking, thereby reducing the braking performed by the vehicle brakes and prolonging brake pad life. This would also decrease fuel consumption.